The present invention relates to new catalysts for use in dehydrogenation reactions and, particularly, in the dehydrogenation of saturated or monoethylenic aliphatic hydrocarbons of low molecular weight (containing, for example, from 2 to 8 carbon atoms) as well as in the dehydrogenation of alkylaromatic hydrocarbons (such as ethylbenzene or diethylbenzenes) to vinylaromatic hydrocarbons (such as styrene or divinylbenzene). It also relates to the manufacture of catalysts and to their use in dehydrogenation processes.
It is known that, in the dehydrogenation of the above-mentioned hydrocarbons, the hydrocarbon is passed, preferably with an additional high proportion of steam (1 to 30 moles H.sub.2 O/mole hydrocarbon), over a catalyst at an hourly rate by volume, expressed in relation with the liquid hydrocarbon, from 0.05 to 5, preferably from 0.1 to 1 volume (STP) per volume of catalyst and per hour and at a temperature of about 450.degree. to 750.degree. C.
Prior art catalysts have been described for dehydrogenating olefinic hydrocarbons, such as butenes (to butadiene) or alkylaromatic hydrocarbons, such as ethylenebenzene (to styrene), these catalysts containing a major proportion of weight of iron oxide, a potassium compound (oxide or carbonate), vanadium oxide, optionally chromium oxide, as well as a small proportion (from 0.01 to 10% by weight) of at least one additional oxide of a metal such as aluminium, cadmium, copper, magnesium, manganese, nickel, rare earth metals, uranium and zinc. Such catalysts are disclosed in particular in the French Pat. No. 2 387 200 which substantially corresponds to the U.S. Pat. Nos. 4,143,083 and 4,152,300. In these patents, the rare earth metals are defined as metals of atomic number from 58 to 71 included, i.e. from cerium to lutetium. The rare earth metals in the examples are cerium, praseodymium and neodymium.
It has now been discovered as advantageous to use as a rare earth metal, in this type of catalyst, lanthanum (of atomic number 57), which improves the catalytic properties in dehydrogenation reactions (particularly of ethylbenzene to styrene) at low cost.
The French Pat. No. 2 270 003, which corresponds substantially to the U.S. Pat. No. 4,134,858, discloses the use of a clayish material in the manufacture of a dehydrogenation catalyst, mainly based on iron, chromium and potassium oxides. During the thermal activation, at a convenient temperature, generally between 850.degree. and 1100.degree. C., the clayish material combines with potassium oxide to form a double aluminium and potassium silicate (more particularly kaliophyllite). This technique enables one to decrease the filling density of the catalyst.